Here's why:

* Plate Tectonics: The Earth's outer layer is made up of tectonic plates that are constantly moving.

* Divergent Boundaries: Mid-ocean ridges are divergent plate boundaries. This means the plates are moving apart.

* Magma Upwelling: As the plates pull away, magma from the Earth's mantle rises up to fill the gap.

* Cooling and Solidification: This magma cools and solidifies, forming new oceanic crust.

* Seafloor Spreading: This process is called seafloor spreading, and it continually adds new crust to the ocean floor.

So, the mid-ocean ridges are essentially "factories" for new oceanic crust!